Description: This function lists the defined node sets in a pop-up window. The user can then select the current set from those listed.
Usage:
1. DSI prompts:
> SELECT SET FROM NODE SET LIST
? [List of all node sets]
CURSOR AT NODE
EXIT
2. Once the set(s) is selected, DSI prompts:
> SET X IS SELECTED
> SET X FLAGGED AS CURRENT SET.